Shortness of breath

Shortness of breath, also known as dyspnea, is the feeling that one cannot breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity", and recommends evaluating dyspnea by assessing the intensity of the distinct sensations, the degree of distress involved, and its burden or impact on activities of daily living. Distinct sensations include effort/work, chest tightness, and air hunger (the feeling of not enough oxygen).[1]

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The American Thoracic Society defines dyspnea as: "A subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity."[6] Other definitions describe it as "difficulty in breathing",[7] "disordered or inadequate breathing",[8] "uncomfortable awareness of breathing",[3] and as the experience of "breathlessness" (which may be either acute or chronic).[2][5][9]

Asthma is the most common reason for presenting to the emergency room with shortness of breath.[2] It is the most common lung disease in both developing and developed countries affecting about 5% of the population.[2] Other symptoms include wheezing, tightness in the chest, and a non productive cough.[2]
Inhaled corticosteroids are the preferred treatment for children, however these drugs can reduce the growth rate.[14] Acute symptoms are treated with short-acting bronchodilators.

Anemia that develops gradually usually presents with exertional dyspnea, fatigue, weakness, and tachycardia.[15] It may lead to heart failure.[15] Anaemia is often a cause of dyspnea. Menstruation, particularly if excessive, can contribute to anaemia and to consequential dyspnea in women. Headaches are also a symptom of dyspnea in patients suffering from anaemia. Some patients report a numb sensation in their head, and others have reported blurred vision caused by hypotension behind the eye due to a lack of oxygen and pressure; these patients have also reported severe head pains, many of which lead to permanent brain damage. Symptoms can include loss of concentration, focus, fatigue, language faculty impairment and memory loss.[citation needed]

It is thought that three main components contribute to dyspnea: afferent signals, efferent signals, and central information processing. It is believed the central processing in the brain compares the afferent and efferent signals; and dyspnea results when a "mismatch" occurs between the two: such as when the need for ventilation (afferent signaling) is not being met by physical breathing (efferent signaling).[17]

Afferent signals are sensory neuronal signals that ascend to the brain. Afferent neurons significant in dyspnea arise from a large number of sources including the carotid bodies, medulla, lungs, and chest wall. Chemoreceptors in the carotid bodies and medulla supply information regarding the blood gas levels of O2, CO2 and H+. In the lungs, juxtacapillary (J) receptors are sensitive to pulmonary interstitial edema, while stretch receptors signal bronchoconstriction. Muscle spindles in the chest wall signal the stretch and tension of the respiratory muscles. Thus, poor ventilation leading to hypercapnia, left heart failure leading to interstitial edema (impairing gas exchange), asthma causing bronchoconstriction (limiting airflow) and muscle fatigue leading to ineffective respiratory muscle action could all contribute to a feeling of dyspnea.[17]

Efferent signals are the motor neuronal signals descending to the respiratory muscles. The most important respiratory muscle is the diaphragm. Other respiratory muscles include the external and internal intercostal muscles, the abdominal muscles and the accessory breathing muscles.

As the brain receives its plentiful supply of afferent information relating to ventilation, it is able to compare it to the current level of respiration as determined by the efferent signals. If the level of respiration is inappropriate for the body's status then dyspnea might occur. There is also a psychological component to dyspnea, as some people may become aware of their breathing in such circumstances but not experience the typical distress of dyspnea.[17]

A number of scales may be used to quantify the degree of shortness of breath.[18] It may be subjectively rated on a scale from 1 to 10 with descriptors associated with the number (The Modified Borg Scale).[18] Alternatively a scale such as the MRC breathlessness scale might be used – it suggests five grades of dyspnea based on the circumstances in which it arises.[19]

A number of labs may be helpful in determining the cause of shortness of breath. D-dimer, while useful to rule out a pulmonary embolism in those who are at low risk, is not of much value if it is positive, as it may be positive in a number of conditions that lead to shortness of breath.[13] A low level of brain natriuretic peptide is useful in ruling out congestive heart failure; however, a high level, while supportive of the diagnosis, could also be due to advanced age, renal failure, acute coronary syndrome, or a large pulmonary embolism.[13]

Individuals can benefit from a variety of physical therapy interventions.[21] Persons with neurological/neuromuscular abnormalities may have breathing difficulties due to weak or paralyzed intercostal, abdominal and/or other muscles needed for ventilation.[22] Some physical therapy interventions for this population include active assisted cough techniques,[23] volume augmentation such as breath stacking,[24] education about body position and ventilation patterns[25] and movement strategies to facilitate breathing.[24]Pulmonary rehabilitation may alleviate symptoms in some people, such as those with COPD, but will not cure the underlying disease.[26][27] Fan therapy to the face has been shown to relieve shortness of breath in patients with a variety of advanced illnesses including cancer. [28] The mechanism of action is thought to be stimulation of the trigeminal nerve.

Systemic immediate release opioids are beneficial in emergently reducing the symptom of shortness of breath due to both cancer and non cancer causes;[3][29] long-acting/sustained-release opioids are also used to prevent/continue treatment of dyspnea in palliative setting. There is a lack of evidence to recommend midazolam, nebulised opioids, the use of gas mixtures, or cognitive-behavioral therapy.[30]

Shortness of breath is the primary reason 3.5% of people present to the emergency department in the United States. Of these individuals, approximately 51% are admitted to the hospital and 13% are dead within a year.[31] Some studies have suggested that up to 27% of people suffer from dyspnea,[32] while in dying patients 75% will experience it.[17] Acute shortness of breath is the most common reason people requiring palliative care visit an emergency department.[3]

In English, the various -pnea-suffixed words commonly used in medicine do not follow one clear pattern as to whether the first syllable or the /niː/ syllable is stressed; the p is usually expressed but is sometimes silent. The following collation shows the preponderance of how major dictionaries transcribe them (less-used variants are omitted):

^Mukerji, Vaskar (1990). "11". Dyspnea, Orthopnea, and Paroxysmal Nocturnal Dyspnea. Butterworth Publishers. Archived from the original on 27 April 2018. Retrieved 15 August 2014. In addition, dyspnea may occur in febrile and hypoxic states and in association with some psychiatric conditions such as anxiety and panic disorder.Cite uses deprecated parameter |deadurl= (help)